1. Field of the Invention
This invention relates to a process for cracking hydrocarbons over transition metal oxide catalysts having Bronsted acidity. More particularly, this invention relates to cracking hydrocarbons by contacting same, at elevated temperature, which a solid acid catalyst having primarily Bronsted acidity which comprises at least one catalytic metal oxide component selected from the Group consisting essentially of oxides of (a) tungsten, niobium and mixtures thereof and (b) mixtures of (a) with tantalum, hafnium, chromium, titanium, zirconium and mixtures thereof, on a pyrogenic alumina support.
2. Background of the Disclosure
U.S. Pat. Nos. 4,269,737, 4,233,139 and 4,244,811 disclose solid acid catalysts comprising certain supported transition metal oxides, their preparation and use as acid cracking catalysts. The supports are refractory metal oxides which are not in themselves acid cracking catalysts, but which when combined with the transition metal oxide component result in acid cracking catalysts. These catalysts are taught as having enhanced activity and selectivity towards forming liquid products compared to conventional acid catalysts. They also exhibit remarkable resistance to coke make and have unusual steam stability. In fact, in some cases it is preferred to pre-steam these catalysts prior to use in order to stabilize the surface thereof. Although steaming these catalysts initially results in a decrease of both surface area and strong acid sites, the steaming itself serves to stabilize the remaining surface area and acidity which is not substantially adversely affected by subsequent steaming. The catalysts described in these patents exhibit primarily Lewis acidity.